Device and Method for Examining the Retinal Vascular Endothelial Function

ABSTRACT

The invention relates to a device and a method for examining the retinal vascular endothelial function of the vessels of the retina at the fundus (F) of a patient&#39;s eye. Using a fundus camera, the vessels of the retina are stimulated with flicker light during a stimulation phase and sequences of images of areas of the fundus (F) are recorded, from which vascular parameters are derived which describe the retinal vascular endothelial function of the vessels. By imaging a macula aperture (MB), which covers the macula, onto the fundus (F), the fundus (F) can be illuminated with a higher light intensity, which improves the stimulation effect and the image quality and/or reduces the strain on the patient.

RELATED APPLICATIONS

This application claims priority to German Patent Application No. DE 102018 107 625.8, filed Mar. 29, 2018, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The area of application of the invention relates to the entire field ofvascular medicine, e.g. ophthalmology, neurology, cardiology,nephrology, diabetology, and hypertensiology.

BACKGROUND OF THE INVENTION

It is known from studies that microvascular changes are frequently of asystemic nature, i.e. they occur similarly in the vessels, in particularthe microcirculation vessels of all organs in the human and animal body,and, depending on the organ, lead to different manifestations ofcardiovascular conditions, such as atherosclerosis, arteriosclerosis,cardiac insufficiency, renal insufficiency, eye conditions, e.g.retinopathies and glaucoma, cerebrovascular conditions, e.g. vasculardementia, and may ultimately trigger or are predictors of cardiovascularevents, such as myocardial infarction and stroke.

As a unique optical window to microcirculation, the eye allows theretinal vessels to be examined as a mirror image of the vessels andtheir functions in inaccessible regions of the other organs in the body.A preferred area of application of the invention consists insupplementing vascular diagnostics of the large vessels with thevascular diagnostics of microcirculation and, in particular, thefunction diagnostics of the vascular endothelial function or vasculardysregulation, respectively.

In ophthalmology, imaging techniques are currently used, above all, inclinical examinations of structural or morphological changes in the eye,in particular in the ocular fundus (in the retina). This includesconventional fundus cameras, OCTs and laser scanners. Vascularexamination by means of static vessel analysis, e.g. using the VesselMapavailable from Imedos, has begun to penetrate everyday clinical practicein microvascular risk stratification and therapy monitoring.

So far, functional examination of the retinal vessels has been appliedonly in research, e.g. devices and methods for measuring blood velocityand vessel diameters on the basis of indicators, based on Doppler or OCTmeasurements as well as systems for dynamic vessel analysis. The areasof application of Doppler- or OCT-based systems provide statements whichhave hardly achieved any significance outside ophthalmology and do notenable function diagnostics of autoregulation or of the endothelialfunction, respectively.

Dynamic vessel analysis enables the examination of variousautoregulation mechanisms on the basis of continuous measurements of thevessel diameters over time and along the location of the large arteriesand veins of microcirculation. The retinal vessels and microcirculation,respectively, are stimulated or provoked during the measurement andrecording of the vessel diameters and respond accordingly byconstriction or dilation, which describes the vessel response of theretinal autoregulation addressed by the respective type of stimulationor provocation and its functionality.

Such stimulation or provocation methods allow examination of variousautoregulation mechanisms of microcirculation. One of saidautoregulation mechanisms is flow-induced autoregulation. In this case,stimulation is effected by flicker light (rhythmic interruption of theflicker light at a defined frequency), but owing to the technologicalshortcomings of the measuring light being simultaneously used as theflicker light, the parameters for the measuring light and the flickerlight are not independently adjustable.

The dynamic vessel analysis system constituting the prior art is theRetinal Vessel Analyzer (RVA) or Dynamic Vessel Analyzer (DVA),respectively, from Imedos (Garhofer, G., Bek, T., Böhm, A. G., Gherghel,D., Grunwald, J., Jeppesen, P., Kergoat, H., Kotliar, K., Lanzl, I.,Lovasik, J. V., Nagel, E., Vilser, W., Orgul, S., Schmetterer, L.: “Useof the retinal vessel analyzer in ocular blood flow research”. ActaOphthalmologica 2010: 88: pages 717-722.) The standard provocation usedin the RVA/DVA is flicker light operating at a frequency of 12.5 Hz.White halogen lamp light in the continuous illumination beam path of aconventional fundus camera is spectrally modified to green measuringlight by a bandpass filter and is rhythmically interrupted by anelectro-optical shutter during the fixed stimulation phases of usually20 s. The examination consists of 3 phases, the first phase (baselinephase BP) recording the baseline vessel diameter and being used as areference for computing vessel responses on a percentage basis. Thesecond phase is the stimulation phase (SP), in which the vessel responseto flicker light is recorded. The third phase will be referred to as theposterior phase (NP) because in this phase, the vessel diameter returnsto baseline. The second and third phases are repeated alternately threetimes and the vessel responses are then superimposed upon each other foraveraging and evaluated with respect to the maximum dilation (maximumflicker dilation FD_(max)) and subsequent constriction.

In the prior art these measurements, obtained by the aforementioned DVA,are restricted to the large vessels of microcirculation between 60 and300 μm.

The evaluated parameters of the vessels, such as the maximum flickerdilation FD_(max), as well as other derivable parameters, areinterpreted as biomarkers for the function diagnostics examination ofthe microvascular endothelial function. Erroneously, some authors alsorefer to and interpret the parameters of the vessel response asparameters of neurovascular coupling NVC. However, there is evidencethat, while neurovascular coupling NVC may represent the initialstimulus, the F_(Dmax) of the vessel response of the large vesselsdescribes the function of the vascular endothelial cells, thuscharacterizing the vascular endothelial function, and that the vascularendothelial function or endothelial dysfunction or vasculardysregulation, respectively, can be examined.

The examination technology of the aforementioned DVA is too rigid, andallows neither any extension of the medical examinations by changing thetype and form of light stimulation nor any optimization for sufficientlystable and high dilation responses. Moreover, the inflexibleillumination causes high production costs, additional scattered lightand reflection light, in particular on the vessels, thereby reducing theaccuracy and reliability of the medical statement as well as the rangeof applications in research and clinical practice. The production costis high, the examination puts a strain on the patient and thereproducibility of the parameters of the vessels for individualexamination is still not sufficiently satisfactory. The aforementionedDVA uses a monochromatic digital image sensor and only one spectralwavelength range in green light, which also generates measuring lightand stimulation light. Owing to its principle, the electro-opticalshutter causes a dependence of the modulation on measurement andstimulation light, as a result of which the arrangement can be optimizedeither only for measurement or only for stimulation. However, theoptimization criteria differ greatly between both types of illumination.Furthermore, subjective errors caused by the examiner occur and theexamination places high demands on the examiner in handling the patientand the aforementioned DVA. Moreover, the inflexible and rigid technicalsolution of generating the stimulation light by the DVA yields only alimited range of applications of the DVA in function diagnostics usingflicker light in research and clinical practice.

Further, WO 2005/094668 A1 describes a device for photometricallymeasuring the vessel diameters of smaller vessels. The disclosedtechnical solution allows the measurement of vessel diameters in thearea of the arterioles and venules, provided the vessels in the fundusimage are selectable as vessels. For this purpose, two differentspectral wavelength ranges of a color camera are used. This considerablyincreases the retina's exposure to light. However, another substantialdisadvantage of the disclosed solutions also consists in the fixedillumination-side arrangement of a light modulator in the jointillumination-side beam path of both color channels of the color camera,which likewise only allows flexible temporal modulation andsubstantially restricts the range of applications and adaptivity.Ultimately, the device of the aforementioned WO 2005/094668 A1 has thesame disadvantages as the aforementioned DVA, except for the advantagethat measurements can be performed even on small retinal vessels, whichare significantly larger than capillaries, however.

Another technical solution for measuring capillary “perfusion” isdescribed in the article by Vilser et. al. from 2008 (Vilser, W., Nagel,E., Seifert, B. U., Riemer, T., Weisensee, J., Hammer, M: “Quantitativeassessment of optic nerve head pallor”. Physiological Measurement 29(2008), pages 451-457). Using a dual bandpass filter in the illuminationbeam path of a conventional fundus camera, two spectral regions in thered and green spectral ranges of the white illumination light areselected and assigned to a red color channel and a green color channelof a 3-chip color image sensor such that both selected illumination-sidewavelengths are received separately by the two assigned red and greencolor channels of the color image sensor. Based on the color intensitiesdetected by the pixels of both color channels (red and green), each ofwhich color intensities can be assigned to the same fundus point,quotients are formed and in turn assigned to the fundus location. Theresulting quotient image is then evaluated with respect to the capillaryperfusion on the optic nerve head.

Although this method does not allow representation of the perfusion ofthe optic nerve head, if perfusion is understood to mean the capillaryblood flow, but it provides a measure of the blood volume and, thus, ofthe capillary vessel diameter and the capillarization of the examinedtissue volumes. The disadvantage of this method is that, in contrast tothe description in the aforementioned article, it cannot providefunctional statements about the regulation of capillary perfusion.

SUMMARY OF THE INVENTION

It is the object of the invention to find a method by which anexamination of the retinal vascular endothelial function puts less of astrain on the patient.

It is also the object of the invention to find a device suitable tocarry out the method.

An essential technical feature of a device according to the invention isthat a macula aperture is arranged in its illumination beam path, in aplane conjugated to the fundus.

The prior art assumes that the flicker stimulation in the area of themacula is decisive for the dilation of the large vessels of the retina.According to the invention, however, it is exactly the area of themacula which is covered by a macula aperture on the illumination sideand is, thus, not stimulated by flicker light, which surprisingly doesnot affect the response of the large vessels (vessel response) that areexposed to measurement and flicker light outside the macula.

The following advantages result from the use of the macula aperture:

It drastically reduces the patient's exposure to light, because thelight-sensitive macula remains covered during the examination.

Alternatively, more light can be used in the stimulation and measurementarea not covered by the aperture, i.e. in the light field on the fundusnot covered by the macula aperture, so that the fundus outside themacula can be illuminated with a higher light intensity, which resultsin an improved signal-to-noise ratio, enhances the stimulation effect,increases dilation and significantly improves the image quality in themeasurement area around the macula aperture.

With the macula shaded by the macula aperture, the high brightnesscontrast makes it easier for the patient to find and focus on a fixationmark provided for internal fixation of the foveola. Restless eyemovements interfering with the examination are significantly reduced,which considerably improves the quality of the measurements.

Another advantage is that by centrally arranging the macula aperture,reflections on the ophthalmoscope lens of the fundus camera can beblocked out completely. This also considerably reduces scattered lightaffecting the image, especially scattered light from the central area ofthe superimposed illumination-side and image-side beams, which appearsas irritating, contrast-reducing brightening in the image of the fundus.

Accordingly, complex and expensive optical units connected withanti-reflection measures can be dispensed with in the illumination beampath of the fundus camera. The overall length and the cost of developingand manufacturing the fundus camera can be comparatively reduced.Furthermore, the luminous flux into the eye is reduced.

The macula aperture and optionally, according to the invention, furtherapertures inserted in the illumination beam path provide field areas,within the light field, for the use of further beam paths or beams,which serve the purpose of exact, automatable adjustment of the funduscamera to the eye and, thus, of eliminating sources of errors and areadvantageously usable directly with the digital image sensor of thefundus camera, without additional detectors.

Advantageously, there is a partly transparent web on the maculaaperture. The web serves, on the one hand, as a mechanical holder forthe macula aperture and, on the other hand, as another aperture insertedin the illumination beam path in order to cover the optic nerve head(papilla), so as to optimize the dynamic range of the digital imagesensor of the fundus camera and avoid overexposure by very brightsurface areas of the optic nerve head.

Advantageously, the illumination unit of the fundus camera is anadaptive, geometrically structurable illumination unit, e.g. in the formof an annular LED array. This allows the flicker light and the measuringlight to be generated independently of each other, be it temporally,geometrically, spectrally or with respect to temporal intensity control.

In a device for examination of the retinal vascular endothelial functionof the vessels of the retina at the fundus of an eye, said devicecomprising a fundus camera with an observation beam path including adigital image sensor designed to record image sequences of areas of thefundus, onto which the observation beam path of the fundus camerafocuses, and with an illumination beam path in which an illuminationunit is arranged in a plane conjugated to the pupil of the eye, forillumination of the fundus with a measuring light and a flicker lightwithin a light field on the fundus that is limited by the image of afield aperture, which is arranged in a plane conjugated to the fundus inthe illumination beam path, the object of the invention is achieved inthat at least one macula aperture is arranged in the plane conjugated tothe fundus in the illumination beam path, said aperture being providedwith a respective fixation mark, so that one of the at least one maculaaperture covers the macula on the fundus when the eye fixates on thefixation mark of the one macula aperture.

The macula aperture is advantageously a mechanical aperture or anoptoelectronic aperture, e.g. a transmission display.

Advantageously, exactly one macula aperture is present, which isarranged in the plane conjugated to the fundus in the illumination beampath, and the fixation mark is a punctiform opening in an area center ofthe macula aperture.

Further, a partly transparent web preferably abuts the macula aperture,said web being radially aligned to the area center of the maculaaperture and by which web the papilla at the fundus can be covered, sothat the radiation intensity of an image of the papilla can be adaptedto a dynamic range of the digital image sensor that is designed for theradiation intensity of an image of the areas of the fundus surroundingthe papilla.

Advantageously, another partly transparent aperture, adjustable intransparency, is present to cover the papilla.

The macula aperture is preferably movable in the plane conjugated to thefundus in the illumination beam path, with the area center of the maculaaperture remaining located within the field aperture, so that differentselected areas of the fundus are illuminated by the light field andsequences of images of the different selected areas of the fundus can berecorded.

Preferably, exactly one macula aperture is formed on the field aperturesuch that the fixation mark is located within the field aperture in amanner abutting an inner edge, and the field aperture is rotatable aboutan optical axis of the illumination beam path, so that differentselected areas of the fundus are illuminated by the light field andsequences of images of the different selected areas of the fundus can berecorded.

Another preferred variant consists in that exactly four macula aperturesare formed in diagonally opposite pairs on the field aperture such thatthe respective fixation mark is located within the field aperture in amanner abutting an inner edge, so that different predetermined areas ofthe fundus are illuminated by the light field and, alternatively,sequences of images of the different predetermined areas of the funduscan be recorded.

Advantageously, the illumination unit is formed by an adaptive,structurable arrangement of light sources, in the plane conjugated tothe pupil, which can be switched on and off and/or modulated in theirintensity, regardless of location, spectrum and time and separately.This makes it possible to implement a great diversity of illuminationstructures. When selecting and controlling individual light sources, therespective active (light-emitting) light sources define the geometry,e.g. a ring, a half ring, or ring segments, and the dimension of theillumination structure, e.g. by an internal diameter d_(i) and anexternal diameter d_(a). By driving spectrally different light sources,illumination structures differing in time and space can be formed fordifferent spectral ranges. An illumination unit designed in this manneris an advantageous embodiment of a device according to the invention.However, a device according to the prior art equipped with anillumination unit according to the invention will also achieve theobject of the invention by itself, without a macula aperture.

Preferably, an image of the field aperture arranged in the illuminationbeam path has a smaller cross-section on the digital image sensor than areception surface of the digital image sensor, and the brightnessdistribution in a resulting differential area is used to determine ascattered light distribution by which the images of the image sequencescan be corrected.

In a method for examination of the retinal vascular endothelial functionof the vessels of the retina at the fundus of an eye, said methodcomprising the process steps of adjusting a fundus camera to the eye,generating measuring light for illumination of the vessels of the retinaat the fundus and of flicker light for stimulation of the vessels of theretina at the fundus during a stimulation phase, generating a sequenceof images of an area of the fundus during a baseline phase, at least onestimulation phase and at least one posterior phase, measuring the vesseldiameter of selected vascular segments of the vessels of the retina inthe images of the generated image sequence as a function of location andtime, performing movement correction of the measured vascular segments,wherein each movement-corrected vascular segment is assigned to alocation on the fundus, forming diameter signals, which respectivelyrepresent the measured vessel diameters as a function of the time andlocation of the respectively selected vascular segment, and derivingvascular parameters from the diameter signals, each of said parametersdescribing the endothelial function of the respectively selectedvascular segment, the object is further achieved either in that theillumination and stimulation of the macula at the fundus is prevented bysharply imaging on the fundus at least one macula aperture, on which afixation mark is located, and the eye being aligned with said one maculaaperture by fixation on the fixation mark of one of said at least onemacula apertures such that the macula is covered by an image of said onemacula aperture, or in that the fundus is illuminated by an adaptivelystructurable arrangement of light sources, which can be adapted to therespective opening of the pupil and to other given conditions by agenerated illumination structure and by which the measuring light andflicker light can be adjusted independently of each other.

Advantageously, sequences of images of different selected areas of thefundus are recorded sequentially, in each case after exactly one maculaaperture imaged onto the fundus has been shifted to a differentlocation, so that its image on the fundus has been shifted and the eye,fixating on the fixation mark, has followed.

Further advantageously, the location parameters of the locations of themacula aperture are stored and are retrievable and adjustable again forrepeat and follow-up measurements.

Alternatively, image sequences of different predetermined areas of thefundus are preferably recorded, while four macula apertures, which arearranged diagonally opposite each other, are imaged onto the fundus andthe eye has sequentially fixated on a different one of the fixationmarks in each case.

The durations of the baseline phase, the stimulation phase and theposterior phase and the parameters of the measuring light and of theflicker light are preferably adjusted independently and are stored, in amanner assigned to a patient and to an examination program, so as to beretrievable and adjustable again as a set of parameters for repeat andcomparative examinations.

The maximum flicker dilation is advantageously determined as one of thederived vascular parameters and is output in a measurement reporttogether with a graphical representation of averaged diameter signalsthat are each respectively generated for the selected arterial andvenous vascular segments on the basis of the diameter signals formed forthis purpose.

Advantageously, the maximum flicker dilation is assigned, in acolor-coded manner, to the respective vascular segment in a mappingimage for functional imaging of the endothelial function, wherein amissing vasodilation or a vasodilation below a predetermined thresholdvalue is marked in red and a vasodilation above a threshold value, whichcorresponds to a healthy vascular function, is marked in green on theassociated vascular segment, and the mapping image is output as agraphical examination result.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail with reference to thefollowing exemplary embodiments with the help of drawings, wherein:

FIG. 1 shows a block diagram of a device according to the invention;

FIG. 2 shows an optics diagram of a fundus camera according to theinvention;

FIG. 3 shows an area (light field) of the fundus of an eye illuminatedin a manner limited by the image of a field aperture;

FIG. 4A shows a macula aperture imaged centrally on the fundus;

FIG. 4B shows a macula aperture imaged eccentrically on the fundus;

FIG. 5A shows a macula aperture formed on the field aperture and imagedon the fundus;

FIG. 5B shows four macula apertures formed on the field aperture andimaged on the fundus;

FIG. 6 shows the images of the field aperture as well as of the maculaaperture on the reception surface of the digital image sensor;

FIG. 7A shows a first embodiment example of an illumination unit as anadaptive, structurable arrangement of light sources;

FIG. 7B shows a second embodiment example of an illumination unit as anadaptive, structurable arrangement of light sources;

FIG. 7C shows a third embodiment example of an illumination unit as anadaptive, structurable arrangement of light sources;

FIG. 7D shows a fourth embodiment example of an illumination unit as anadaptive, structurable arrangement of light sources, and

7E shows a fifth embodiment example of an illumination unit as anadaptive, structurable arrangement of light sources.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of a device according to the invention is shown as a blockdiagram in FIG. 1. Similar to a device known from the prior art, thedevice according to the invention comprises a fundus camera 1 with adigital image sensor 2 and an illumination unit 3, a control unit 4, adata and image processing unit 5, a unit for generating diameter signals6, a signal analysis unit 7, a result and presentation unit 8 and aninput and output unit 9. The device differs from a prior art device ofthe same generic type essentially in the design of the fundus camera 1and advantageously in the design of the illumination unit 3.

FIG. 2 shows an optics diagram of a fundus camera 1. The latter includesan illumination beam path 1.1 and an observation beam path 1.2 (imagingbeam path).

In the simplest case, the observation beam path 1.2 has two lenses,namely an ophthalmoscope lens OL and an objective lens CO, via which thefundus F of the eye A, on which the fundus camera 1 has been focused, isimaged into a plane F″, which is conjugated to the fundus F and locatedon a reception surface 2.1 of the digital image sensor 2.

The illumination beam path 1.1 is coupled into the observation beam path1.2 by a pinhole aperture LB and, in the simplest case, includes acollimator lens KL and a field lens FL. The illumination unit 3 isarranged in a plane which is conjugated to the pupil AP and located inthe illumination beam path 1.1 and is imaged into the pupil AP. Thefield aperture FB, which is arranged in a plane F′″ conjugated to thefundus F in the illumination beam path 1.1, is imaged sharply on thefundus F and on the reception surface 2.1 of the digital image sensor 2.

It is essential to the invention that a macula aperture MB is present,in addition, in the illumination beam path 1.1. The macula aperture MBis preferably arranged in a same plane as the field aperture FB, butboth may also be arranged in different planes conjugated to one another.In this case, the macula aperture MB may be arranged in a fixed ormovable manner within the field aperture FB, which is typically formedby a ring. Various advantageous embodiments will be explained withreference to exemplary embodiments.

According to a first exemplary embodiment shown in FIG. 4A, the maculaaperture MB is circular, arranged centrally, i.e. its area center FMP islocated on the optical axis of the illumination beam path 1.1, and isimaged onto the fundus F at a field angle of 15°. For internal fixation,the macula aperture MB has a small opening as a fixation mark FM aroundits area center FMP. As an alternative, instead of using the opening asa fixation mark FM, small light sources, e.g. LEDs, structured aspoints, rings or crosses, may be reflected as luminous fixation marks FMin temporally, geometrically and spectrally different manners,controllable via the control unit 4. On the one hand, this allowsdifferent adjustments to be made of the fundus F with respect to themacula aperture MB, due to said geometric structuring. On the otherhand, flashing fixation marks FM or color changes may increase thepatient's attention or may be adapted to the visual capacity of thepatient's eye. The eye A to be examined may also be fixed by externalfixation, so that no fixation mark FM is required within the funduscamera 1. In particular, if the visual capacity of the eye A to beexamined is so low that it cannot fixate on a fixation mark FM, it makessense to provide to the eye A not to be examined a fixation mark FMwhich is located outside the fundus camera 1 and is positioned to matchthe loation of the macula aperture MB.

FIG. 4B shows the macula aperture MB in a position shifted with respectto FIG. 4A. Accordingly, a different area of the fundus F is now locatedwithin the light field LF, which is limited by the image of the fieldaperture FB on the fundus F.

FIG. 3 schematically shows a structure of the fundus F of an eye A foreasy understanding. It also shows, in addition to large arteries A_(v)(light gray) and large veins V_(v) (dark gray): the macula M, the areawith the highest density of photoreceptors (yellow spot) and, thus, themost light-sensitive area of the fundus F, the foveola V, the foveacentralis at the center of the macula M, by which the eye A fixates on afixation mark FM, and the papilla P (optic nerve head, blind spot), theexit point of the optic nerve from the envelope of the eyeball, which issupplied with relatively little blood.

The field aperture FB and the macula aperture MB are axially movabletogether in the illumination beam path 1.1, allowing the macula apertureMB to be imaged onto the fundus F so as to be sharply visible for thepatient.

Advantageously, a web ST is present, which is radially aligned with thearea center FMP, said web ST serving as a mechanical holder for themacula aperture MB and being rotatable by 180° against the light fieldcenter when changing the eye A to be examined from the right eye A tothe left eye A.

In an advantageous alternative embodiment, the web ST may be so wide andtransparent that it covers the papilla P in order for the intensity ofthe measuring light reflected in the area of the papilla P to beadjusted to the surrounding retina and, thus, to the dynamic range ofthe digital image sensor 2.

In an advantageous design of the exemplary embodiment for furthermedical examinations, means are provided which allow the macula apertureMB to be moved radially in the light field LF. Due to the fact that, byfollowing the fixation mark FM, the eye A to be examined follows themacula aperture MB such that the macula M is always covered by themacula aperture MB, the papilla P and individual selected retinal vesseltrees are arranged more centrally in the light field LF for measurementsand can be examined.

Another advantageous embodiment is the stationary arrangement of one ormore macula apertures MB on the inner edge of the field aperture FB. Theadvantage of such an embodiment is the fast, easy adjustment of thefundus F or of the measuring points, respectively, in a manner which isstandardized for different eyes and which is reproducible for repeatmeasurements.

FIG. 5A shows an embodiment in which a macula aperture MB is firmlyconnected to or designed monolithically with the field aperture FB. Byrotating the field aperture FB about its center, which is located on theoptical axis of the illumination beam path 1.1, the eye A is maximallydeflected in a circulatory movement, allowing a maximum overall area ofthe fundus F to be sequentially illuminated, imaged and, consequently,examined.

FIG. 5B shows an embodiment in which four macula apertures MB are formedon the inner edge of the field aperture FB in opposite pairs or offsetby 90° with respect to each other, respectively. For this case, it isenvisaged for the patient's eye A to fixate sequentially on at least thefixation marks FM of two opposite macula apertures MB, by whichpredetermined areas of the fundus F are illuminated and imaged.

The data and image processing unit 5 is preferably configured such thatthe image of the macula aperture MB, optionally with the web ST, in theimage provided to the examiner is cleanly blocked out electronically bysoftware.

The field aperture FB, which limits a light field LF on the fundus F, ispreferably imaged on the reception surface 2.1 of the digital imagesensor 2 with a smaller cross-section than the cross-section of thereception surface 2.1. In contrast to the prior art, where the size ofthe image of the field aperture FB is regularly adapted to the size ofthe reception surface 2.1 of the digital image sensor 2 and, thus, thereception surface 2.1 is fully illuminated, this generates adifferential area 2.2 outside the image of the fundus F, which can beused to compute the scattered light distribution as well as to monitorthe non-reflecting and low-scatter adjustment of the fundus camera 1 tothe eye A. In this case, it does not matter whether parts of thedifferential area 2.2 are made accessible to the examiner as adjustmentaids or are used for automatic adjustment processes. The data and imageprocessing unit 5 determines the brightness distribution on thereception surface 2.1 of the digital image sensor 2 within the image ofthe macula aperture MB and in the differential area 2.2, therebycomputing the scattered light distribution in the image of the fundus Fon the digital image sensor 2 via an approximation algorithm andcorrecting the image accordingly.

The illumination beam path 1.1 further includes, as the illuminationunit 3 according to the invention, a preferably adaptively structurablecircular or annular arrangement of small light sources, e.g. threegroups of LEDs with different spectral properties, preferably in theblue, green and red spectral ranges, said groups of LEDs being arrangedin the illumination beam path 1.1 in a plane AP″ conjugated to the planeof the pupil AP. By differentiated control of the LEDs, the respectivelycontrolled (active) LEDs form an adaptive illumination structure.

Said LEDs are controlled via the adaptive control unit 4 such that theLED light intensities of the different-colour LEDs are modeledseparately and independently of each other. The modulation of the LEDlight is intended to enable both the adjustment of the intensity ofcontinuous light as measuring light and the adjustment of stimulationlight alternating between high and low intensity, with adjustableparameters of the frequency, the modulation depth and the alternatinglight shape (e.g. wave-shaped to step-shaped, symmetrical orasymmetrical change between bright and dark phases). Also, theillumination structure, which is respectively determined by thetemporally controlled (active) LEDs of a group or of a spectral range,respectively, can be adjusted to the requirements for differentexaminations. For instance, the illumination structure may be formed bythe temporally and locally controlled active LEDs as temporally changingnarrower or wider rings, half rings, ring segments or points, which canbe used to reduce scattered light and reflection light and to adapt theopening of the pupil AP.

The opening of the pupil may differ individually to a great extent,depending on whether the examination is performed in the non-mydriaticor mydriatic mode, also depending on the light conditions and on thepatient. In order to reduce the patient's exposure to light and toprovide optimal conditions for imaging and measurement, an externaldiameter d_(a) of the illumination structure is adapted to the openingof the pupil AP. An internal diameter d, of the illumination structureis adapted to the size of the image AB′ of an aperture stop AB arrangedin the observation beam path 1.2 in a plane AP″ conjugated to the pupilAP. Advantageously, the internal diameter d, of the illuminationstructure is greater than the diameter of the image AB′ of the aperturestop AB. Adapting this radiation-free space between the illuminationlight and the imaging light allows the influence of reflections orscattered light to be reduced as a function of the individual conditionsof the patient's eye.

Also, a structural change rotating during the examination ordifferentiated local control of the LEDs, respectively, may be used tocapture image sequences with different illumination structures, allowingthe angle at which the illumination radiation is incident on a fundusobject (e.g. vessels) to be varied such that vascular reflections arereduced and local image contrasts are increased.

The adaptive adjustment, in particular of the external diameter d_(a) ofthe illumination structure, also allows the dynamic vessel analysis inthe mydiatric mode to be switched very quickly to the mode ofnon-mydriatic static vessel analysis, and vice versa. At the same time,said adaptivity also allows the fundus F to be focused via the principleof Scheiner apertures.

FIGS. 7A to 7E show examples of different embodiments of theillumination unit 3 as an adaptive, structurable arrangement of lightsources.

Each of said figures shows an image of the illumination unit 3 in theplane of the pupil AP together with an image AB′ of the aperture stop ABarranged in the observation beam path 1.2. The illumination unit 3advantageously represents a circular or annular arrangement of LEDs in aring shape.

FIGS. 7B and 7D show comparative views of pupils AP with a large and asmall opening, respectively. The illumination structure, formed byactivated LEDs, which are represented by different types of hatching,and the aperture stop AB, which is embodied, for example, as an iriswith a variable diameter, are adapted such that an optimal luminous fluxenters the eye A or an optimal diameter of the aperture stop AB is setfor high image resolution. Also, when changing the external diameterd_(a) of the illumination structure and accordingly adapting theinternal diameter d_(i) the area of the illumination structure can bekept constant so as to keep the incident luminous flux stable bycompensation. In this case, the external diameter d_(a) is optimallyadapted to the opening of the pupil AP or of the iris, respectively.

FIGS. 7A and 7B show, in comparative views, that the internal diameterd_(i) is opened wide while the opening of the pupil AP remains the same.This produces either a large radiation-free space between theillumination beam, internally limited by the internal diameter d_(i) andthe observation beam, limited by the image AB′ (continuous line in FIG.7B) of the small aperture stop AB, thus achieving a reduction ofscattered light, especially in older patients. Or, for a large aperturestop AB (AB′ as a dashed/dotted line in FIG. 7B), the imaging propertiesare comparatively improved and more light is provided to the digitalimage sensor 2.

In conventional illumination units, there is the frequent problem thatthe illumination beam path is cut off by drooping eyelids, longeyelashes or a slanted eye shape, thereby allowing less light into theeye A, which causes the image quality to deteriorate and may even resultin the examination being aborted. By activating and deactivating LEDs,as shown in FIG. 7E, an illumination structure can be created, whichevades cutoffs. Also, in older patients there is the frequent problem ofcataracts considerably affecting image quality. Even in this case, bychanging the location of the illumination structure, as shown by way ofexample in FIG. 7D, the illumination beam path can be made to bypassmore heavily clouded areas of the eye lens. For this purpose, forexample by controlling such an illumination structure in a rotarymanner, the position of the illumination beam path can be optimized.

Advantageously, also in order to remove irritating vascular reflectionson the ocular fundus or to allow the higher-contrast representation ofvessels and other objects on the ocular fundus, the beam direction ofillumination beams incident on the ocular fundus may be changed bydifferentiated control of the LEDs.

FIG. 7C shows, by way of example, that only the green and red LEDs areactivated which generate the measuring light in the exemplaryembodiment.

Another advantageous alternative embodiment of a digital image sensor 2is a monochromatic image sensor recording color images. For thispurpose, three monochromatic images are respectively combined in quicksuccession, each of said three monochromatic images being assigned adifferent LED color for illumination. The three images are eachsubsequently combined into one color image (image with three assignedcolor channels).

The adaptive control unit 4 is connected to a data and image processingunit 5, which is in turn connected to the digital image sensor 2. Thefrequency of the flicker light (change between bright and dark) iscontrolled by a synchronization signal which, in this exemplaryembodiment, is generated by the digital image sensor 2 and istransmitted to the control unit 4, and is synchronized in order tosynchronize all signals formed during the process steps with the imagesequence recorded by the digital image sensor 2. For the invention, itdoes not matter whether the synchronization signal is given by thedigital image sensor 2 or by the data and image processing unit 5 andcontrols the recording of the images of the image sequence.

The digital image sensor 2 records images of the fundus F at an imagingfrequency of preferably 25 Hz, which preferably results in a flickerfrequency of 12.5 Hz. However, according to the invention, any otherimaging frequency synchronized with a flicker frequency may be used forthe device and the method. In this case, a variable imaging and flickerfrequency may also be used to address different questions.

The data and image processing unit 5 selects the papilla P, the image ofthe macula aperture MB, optionally with the web ST, as well as arterialand venous large vessels of the retina in each image, records themovement coordinates of the fundus F following the fixation mark FM anduses them for movement correction of the images of the image sequence orof the measurement data and signals, respectively.

Furthermore, a unit for generating diameter signals 6 is provided, whichdetermines the vessel diameters in the selected vascular segments andgenerates, for each vascular segment, as a function of time andlocation, diameter signals D(t,x,y) for an image sequence and transmitsthese signals to the signal analysis unit 7. There, the signals of thevascular segments are used to form averaged diameter signals D(t,x,y)for entire vascular sections by averaging after combining severalvascular segments, said signals being graphically displayed and outputto the examiner for presentation. In the signal analysis unit 7, typicalparameters of the vessels, describing the endothelial function, such as,for example, the maximum flicker dilation FD_(max) in the stimulationphase SP, are also computed and output via the result and presentationunit 8 and the input and output unit 9. The result and presentation unit8 additionally serves to generate mapping images.

The method according to the invention will be explained below withreference to an exemplary embodiment.

Step 0:

An examination program menu for different examinations relating todifferent medical questions is presented to the examiner. The selectionof examination parameters serves to adjust the arrangement of the atleast one macula aperture MB, the parameters of the fixation light,provided the fixation mark FM is formed by a self-luminous mark, theparameters of the measuring light and the parameters of the flickerlight.

The examiner can choose between adjusting

0-1: freely selected parameters (free parameter selection),

0-2: comparative parameters (comparative mode), and

0-3: repetition parameters (repeat mode),

as described in the following process steps:

Step 0-1: Free Parameter Selection

For questions in research, free parameter selection is often useful. Thefollowing parameters are preferably presented to the examiner forautomatic pre-selection, and after selection the set of parameters isstored as a new program for comparative and repeat examinations under aname to be assigned by the examiner.

Step 0-1-1: Adjustment of the Type and Location of the Macula ApertureMB as Well as of the Fixation Point (Fixation Parameters)

The type and location of the one or more macula apertures MB and,optionally, of the web ST are displayed to the examiner as an image formanual adjustment or preset automatically.

The examiner then selects the type of fixation by setting the followingfixation parameters for the fixation mark FM:

-   -   spectral determination of the geometric fixation structure        (cross, point, ring . . . )    -   determination of the fixation color    -   determination of the fixation intensity    -   determination of the temporal changes in fixation intensity        (e.g. flash frequency)    -   or use of an opening in the macula aperture MB as a fixation        mark FM, which is illuminated by the flicker and measuring light

Step 0-1-2: Adjustment of the Measuring Light (Measuring LightParameters)

-   -   determination of the spectral range (preferably green); for        special issues, measuring light from different spectral ranges        may also be used    -   determination of the intensity (manually or automatically        re-adjustable, controlled by image brightness)    -   determination of the time response during the stimulation phase        SP

In this manner, the flicker light for stimulation and the measuringlight may be synchronized with each other, independently, for themedical issue.

Step 0-1-3: Adjustment of the Flicker Light Parameters

-   -   Adjustment to luminance flicker or color flicker

For luminance flicker, the defined spectral range of the flicker lightis modulated only in accordance with the other flicker parameters. Inthe case of color flicker, the flicker light only changes the spectralrange with the flicker frequency, which means mutual switching of thedifferent-color LEDs.

-   -   the adjustment of the spectral ranges of the color LEDs is        performed in accordance with the flicker type, e. g. in the case        of color flicker, the flicker light is set to change from a blue        LED to a green LED    -   adjustment of the modulation of the flicker light (modulation        parameters)

In the present example, the examiner may define the form of stimulationfor each half-period of the flicker light with the following parameters:

-   -   intensity maximum

intensity minimum

modulation depth

-   -   intensity increase    -   intensity decrease    -   duration of the intensity maximum    -   wave-shaped or step-shaped modulation

Step 0-1-4: Adjustment of the Examination Phases (Phase Parameters)

-   -   this involves adjustment of the duration of the examination        phases: baseline phase BP, stimulation phase SP, and posterior        phase NP    -   in the case of an adaptive stimulation phase SP, adjustment is        performed:        -   of a minimum duration of the stimulation phase SP        -   of a maximum duration of the stimulation phase SP        -   and of the abort parameters for the stimulation period

Step-0-1-5:

All freely selected parameters are combined in a set of parameters andstored with a special examination name and presented upon renewedselection of the examination menu

Step 0-2: Comparative Mode (Ensures the Same Examination Conditions forDifferent Eyes a for the Same Medical Question)

The desired examination program for the medical question is selectedfrom the examination menu and the respective set of parameters for theselected examination program is loaded. The LEDs of the device arecontrolled accordingly via provided control algorithms, therebyadjusting the measuring light and the flicker light to the selectedexamination program in a variable and adaptive manner

Step 0-3: Repeat Mode (Ensures the Same Examination Conditions inFollow-Up Sessions for the Same Eye A) with Reference MeasurementLocations

The eye A already examined previously is selected from thepatient-related database, with both the data sets stored for theselected vessels and the set of parameters of the examination performedbeing preset.

During the adjustment of the device to the eye A, the movementcorrection ensures an exact match of the recorded areas of the fundus Fbetween the sessions.

After adjustment of all parameters, the examination procedure begins.

Step 1:

The patient's head is held in place by a head and chin rest. The patientis asked to look at the fixation mark FM on the dark macula aperture MB.

Step 2:

The device is adjusted to the eye A to be examined, by means of a crosstable so as to result in a low-scatter and non-reflecting image of thefundus F.

Step 3:

The image of the fundus F and the macula aperture MB are focused, and byrotating the web ST, the web ST of the macula aperture MB is positionedsuch that it covers the papilla P of the eye A to be examined

Step 4:

The measuring process of the examination is started as soon as recordingof an image sequence begins during the baseline phase BP, wherein onlymeasuring light, and no flicker light, is used.

Step 5:

By Algorithms

-   -   5.1: the position of the web ST in the light field LF is        detected and, thus, the examined eye A (right or left) is        automatically identified.    -   5.2: the central residual reflections of the ophthalmoscope lens        OL are detected centrally and blocked out electronically.    -   5.3: the image of the first field aperture FB of the        illumination beam path 1.1 of the fundus camera 1 is identified        on the fundus F.    -   5.4: the scattered light distribution outside the light field LF        and in the area not blocked out by the macula aperture MB is        computed and subtracted from the recorded image of the fundus F.    -   5.5: the images are movement-corrected with respect to the eye        movements.    -   5.6: the papilla P is selected and blocked out, e.g. for        applications in static vessel analysis.    -   5.7: the large arterial and venous vessels of the uncovered        retina are selected and stored.

Step 6:

Algorithms for diameter measurement are used to determine vesseldiameters along the selected vessels, one vascular segment afteranother, stored in location-corrected form and assigned to thesynchronization signal and, consequently, to the individual images ofthe image sequence. Based on this data, diameter signals D(t,x,y) areformed for each vascular segment.

Step 7:

First, the baseline phase BP is started with a baseline time. This isautomatically followed by the stimulation phase SP with the stimulationtime (flicker period) and the set of parameters provided for the flickerlight.

Step 8:

During the stimulation phase SP, all vascular signals are normalized totheir respective average baseline value (determined on the basis of thebaseline phase BP) on a percentage basis. The flicker-induced changes inall vascular signals during the stimulation phase SP are averagedseparately for arteries A_(v) and veins V_(v) and evaluated with respectto their scatter and dilation. According to the invention, whenselecting the adaptive stimulation phase SP, the stimulation time ismade dependent on the examination result. If the increase in flickerdilation and the scatter of the average flicker dilation is below apredetermined threshold value after 20 s, the stimulation phase SP isterminated.

The average flicker dilation of all arterial and venous vascularsegments is output separately.

Step 9:

After terminating the stimulation phase SP, the posterior phase NP ofthe examination begins, the flicker light is deactivated and thecontinuous measurements are continued until the posterior phase NP isterminated after the preset time. The posterior phase NP may also beconfigured to be adaptive by terminating it when the average signalchanges and the scatter of the signal values are below a threshold valueor another criterion is used for termination. The stimulation phase SPand the posterior phase NP may be repeated alternately several times,preferably three times, for averaging the signals.

Step 10:

Further average parameters, such as e.g. average parameters ofvasomotion in the baseline or the constriction following the decrease indilation, are formed from the diameter signals D(t,x,y) over allvascular segments, separately for arteries A_(v) and veins V_(v).

Step 11:

An average arterial and an average venous vascular signal D=f(t) areformed over all vascular segments and output as an examination resulttogether with the average parameters in an examination report.

Step 12:

For each parameter, in particular for the maximum flicker dilationFD_(max) of the arterial and venous vascular segments, the values havecolors assigned to them, which are then represented as functionalimaging in the image of the fundus F, superimposed in the correctposition. Red segments identify a missing maximum flicker dilationFD_(max) and green segments identify a healthy maximum flicker dilationFD_(max).

It does not matter for the method according to the invention if theadjustment and certain process steps of the evaluation are performedmanually or automatically.

An advantageous embodiment of the device and method according to theinvention is the optoelectronic realization of the macula aperture MBand further apertures in the plane F′″ conjugated to the fundus F in theillumination beam path 1.1, e.g. by a transmission display whose pixelsare independently electronically adjustable in their transmission.During the method of the invention, the display is then controlled bysoftware in accordance with the individual process steps, analogous tothe adjustment of a mechanical macula aperture MB.

LIST OF REFERENCE NUMERALS

-   -   NVK neurovascular coupling    -   RVA Retinal Vessel Analyzer from Imedos    -   DVA Dynamic Vessel Analyzer from Imedos    -   D(t,x,y) diameter signal as a function of time and location x, y        on the fundus F    -   FD_(max) maximum flicker dilation    -   BP baseline phase (recording of the signals without stimulation)    -   SP stimulation phase (recording of the signals during        stimulation)    -   NP posterior phase (recording of the signals after stimulation)    -   1 fundus camera    -   1.1 illumination beam path    -   1.2 observation beam path    -   2 digital image sensor    -   2.1 reception surface    -   2.2 differential area    -   3 illumination unit    -   4 control unit    -   5 data and image processing unit    -   6 unit for generating diameter signals    -   7 signal analysis unit    -   8 result and presentation unit    -   9 input and output unit    -   A eye    -   F fundus    -   M macula    -   P papilla    -   V foveola    -   V_(v) vein    -   A_(v) artery    -   AP pupil    -   MB macula aperture    -   FMP area center of the macula aperture    -   FM fixation mark    -   ST web    -   FB field aperture    -   KL collimator lens    -   FL field lens    -   OL ophthalmoscope lens    -   CO objective lens    -   LB pinhole aperture    -   AB aperture stop in the observation beam path 1.2    -   AB′ image of the aperture stop AB in the pupil AP    -   F′″ plane conjugated to the fundus F in the illumination beam        path 1.1    -   F′, F″ planes conjugated to the fundus F in the observation beam        path 1.2    -   AP″ plane conjugated to the pupil AP in the illumination beam        path 1.1    -   AP′ plane conjugated to the pupil AP in the observation beam        path 1.2    -   LF light field    -   d_(i) internal diameter of an illumination structure    -   d_(a) external diameter of an illumination structure

What is claimed is:
 1. A device for examination of retinal vascularendothelial function of vessels of a retina at a fundus (F) of an eye(A), said device comprising: a fundus camera defining an observationbeam path, the fundus camera comprising a digital image sensor designedto record image sequences of images of areas of the fundus (F), theobservation beam path focusing onto the fundus (F), and defining anillumination beam path; an illumination unit being arranged in a plane(AP″) conjugated to a pupil (AP) of the eye (A) in the illumination beampath, the illumination unit serving to illuminate the fundus (F) with ameasuring light and a flicker light within a light field (LF) on thefundus (F) that is limited by an image of a field aperture (FB), thefield aperture (FB) being arranged in a plane (F′″) conjugated to thefundus (F) in the illumination beam path; and at least one maculaaperture (MB) being arranged in the plane (F′″) conjugated to the fundus(F) in the illumination beam path, said at least one macula aperture(MB) being provided with a respective fixation mark (FM) so that the atleast one macula aperture (MB) covers a macula (M) on the fundus (F)when the eye (A) fixates on the fixation mark (FM) of the at least onemacula aperture (MB).
 2. The device according to claim 1, wherein the atleast one macula aperture (MB) is a mechanical aperture.
 3. The deviceaccording to claim 1, wherein the at least one macula aperture (MB) isan optoelectronic aperture.
 4. The device according to claim 3, whereinthe at least one macula aperture (MB) is a transmission display.
 5. Thedevice according to claim 2, wherein only one macula aperture (MB) ispresent, the only one macula aperture being arranged in the plane (F′″)conjugated to the fundus (F) in the illumination beam path, and whereinthe fixation mark (FM) is a punctiform opening in an area center (FMP)of the macula aperture (MB).
 6. The device according to claim 5, furthercomprising a partly transparent web (ST) abutting the only one maculaaperture (MB), said web (ST) being radially aligned to the area center(FMP) of the only one macula aperture (MB), the web (ST) serving tocover the papilla (P) at the fundus (F), so that the radiation intensityof an image of the papilla (P) can be adapted to a dynamic range of thedigital image sensor designed for the radiation intensity of an image ofthe areas of the fundus (F) surrounding the papilla (P).
 7. The deviceaccording to claim 6, further comprising another partly transparentaperture being adjustable in transparency and serving to cover thepapilla (P).
 8. The device according to claim 6, wherein the only onemacula aperture (MB) is movable in the plane (F′″) conjugated to thefundus (F) in the illumination beam path, the area center (FMP) of theonly one macula aperture (MB) remaining located within the fieldaperture (FB) to illuminate different selected areas of the fundus (F)by the light field (LF) and to record image sequences of images of thedifferent selected areas of the fundus (F).
 9. The device according toclaim 1, wherein only one macula aperture (MB) is formed on the fieldaperture (FB) such that the fixation mark (FM) is located within thefield aperture (FB) in a manner abutting an inner edge of the fieldaperture (FB), and wherein the field aperture (FB) is rotatable about anoptical axis of the illumination beam path to illuminate differentselected areas of the fundus (F) by the light field (LF) and to recordsequences of images of the different selected areas of the fundus (F).10. The device according to claim 1, wherein four macula apertures (MB)are formed in diagonally opposite pairs on the field aperture (FB) suchthat the respective fixation mark (FM) is located within the fieldaperture (FB) in a manner abutting an inner edge to illuminate differentpredetermined areas of the fundus (F) by the light field (LF) and torecord sequences of images of the different predetermined areas of thefundus (F).
 11. The device according to claim 1, wherein theillumination unit is formed by an adaptive, structurable arrangement oflight sources to implement different illumination structures in theplane (AP″) conjugated to the pupil (AP), the light sources beingswitchable on and off and/or capable of modulation together orseparately of their intensity, spectrum, and time regardless of theirlocation.
 12. The device according to claim 1, wherein an image of thefield aperture (FB) arranged in the illumination beam path has a smallercross-section on the digital image sensor than that on a receptionsurface of the digital image sensor, and wherein a brightnessdistribution in a resulting differential area is used to determine ascattered light distribution by which the images of the image sequencescan be corrected.
 13. A method for examining a retinal vascularendothelial function of vessels of a retina at a fundus (F) of an eye(A), the method comprising: adjusting a fundus camera to the eye (A);generating measuring light for illuminating the vessels of the retina atthe fundus (F) and for illuminating flicker light for stimulation of thevessels of the retina at the fundus (F) during a stimulation phase (SP);generating an image sequence of images of an area of the fundus (F)during a baseline phase (BP), at least one stimulation phase (SP) and atleast one posterior phase (NP); measuring vessel diameters of selectedvascular segments of the vessels of the retina in the images of theimage sequence as a function of location and time; performing movementcorrection for the vascular segments, wherein each vascular segment isassigned to a location on the fundus (F) in a movement-corrected manner;forming diameter signals (D(t,x,y)) representing the measured vesseldiameters as a function of the time and location of each selectedvascular segment; and deriving vascular parameters from the diametersignals (D(t,x,y)), each of said vascular parameters describing theendothelial function of a respectively selected vascular segment;wherein illuminating and stimulating a macula (M) at the fundus (F) isprevented by projecting a sharp image of at least one macula aperture(MB) with a fixation mark (FM) attached to it onto the fundus (F), andaligning the eye (A) with said one macula aperture (MB) by fixation onthe fixation mark (FM) of one of the at least one macula aperture (MB)such that the macula (M) is covered by an image of said one maculaaperture (MB).
 14. The method according to claim 13, further comprisingsequentially recording image sequences of images of different selectedareas of the fundus (F) at any one time after only one macula aperture(MB) imaged onto the fundus (F) has been shifted to a different locationso that its image on the fundus (F) has been shifted and the eye (A),fixating on the fixation mark (FM), has followed.
 15. The methodaccording to claim 14, further comprising storing location parameters ofthe locations of the macula aperture (MB), the location parameters beingretrievable and adjustable for repeat and follow-up measurements. 16.The method according to claim 13, alternatively comprising recordingimage sequences of different predetermined areas of the fundus (F) whileimaging four macula apertures (MB) diagonally arranged opposite eachother onto the fundus (F), and sequentially fixating the eye (A) on adifferent fixation mark (FM) in each case.
 17. The method according toclaim 13, further comprising independently adjusting durations of thebaseline phase (BP), the stimulation phase (SP), the posterior phase(NP), and the parameters of the measuring light and of the flicker lightand storing them in a manner assigned to a patient and to an examinationprogram in order to be retrievable and adjustable again as a set ofparameters for repeat and comparative examinations.
 18. The methodaccording to claim 13, further comprising determining a maximum flickerdilation (FD_(max)) as one of the derived vascular parameters, themaximum flicker dilation (FD_(max)) being an output in a measurementreport together with a graphical representation of averaged diametersignals (D(t,x,y)), the averaged diameter signals (D(t,x,y)) each beingrespectively generated for the selected arterial and venous vascularsegments on the basis of the diameter signals (D(t,x,y)).
 19. The methodaccording to claim 18, further comprising assigning in a color-codedmanner the maximum flicker dilation (FD_(max)) to the respectivevascular segment in a mapping image for functional imaging of theendothelial function, wherein a missing vasodilation or a vasodilationbelow a predetermined threshold value is marked in red and avasodilation above a threshold value corresponding to a healthy vascularfunction is marked in green on the associated vascular segment, andwherein the mapping image is serves as an output of a graphicalexamination result.